For, inter alia, advertising purposes use is made of so-called display units comprising at least one translucent wall surface for supporting a large-size transparency film, and lamp fittings which are mounted internally and connectible to a current source. It also constitutes prior art to form such display units by mechanically and electrically interconnecting a number of light boxes, each having at least one translucent wall surface for supporting a large-size transparency film and each having at least one lamp fitting which can be turned on. Prior-art display units of the last-mentioned type are designed in a manner which requires a considerable expert knowledge and an electrician for mounting and connecting operations. As a result, such display units have not become so widely spread and used as they deserve.